Mass spectrometry methods are very useful for characterizing and/or quantifying chemical, biological and biochemical entities. Tandem mass spectrometry (MS/MS) methods have been shown to be particularly useful for characterizing individual components of a mixture and/or obtaining enhanced structural information from analytes that yield limited fragmentation.
In a typical MS/MS configuration, an ion of a specific mass to charge ratio (m/z) is selected in a first mass analyzer, and transferred to a collision cell where an inert gas is introduced to collide with the selected ion to generate fragmentation. The ions thus formed are then analyzed by a second mass analyzer to obtain a mass spectrum.
In U.S. Pat. No. 5,847,386, Thompson et al. suggest using tapered quadrupole rods to create an axial field in the collision cell of a quadrupole tandem mass spectrometer to facilitate movement of ions through a low energy system.
In U.S. Pat. No. 6,833,544, Campbell et al. disclose use of a linear ion trap component in a mass spectrometer system as a collision cell for collision induced dissociation. Campbell discloses use of segmented rods to form a gradient to move ions through a collision cell.
However, the need remains for improved apparatus and methods for processing ions in mass spectrometry.